1. Field of the Invention
The invention relates to a further continuous process for preparing alkylamino(meth)acrylamides (C) by continuously aminolysing, for example, methyl (meth)acrylate (A) with amines (B) to release methanol (D) by the following reaction equation:
where:    R1=hydrogen or methyl    R2 is a linear, branched or cyclic alkyl radical, an aryl radical which may also be substituted by one or more alkyl groups; the linear, cyclic or branched alkyl radical may have a length of 2-12 carbon atoms, for example ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, hexyl, heptyl, octyl, isooctyl, nonyl, decyl, undecyl, and may optionally be mono- or polysubstituted by            NR3R4 or        OR5;             either R3 or R4 may assume the definition of hydrogen, and in addition:            R1, R4 and R5 may be either the same or different and be an alkyl group having 1-12 carbon atoms, for example methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, hexyl, heptyl, octyl, isooctyl, nonyl, decyl, undecyl or hydrogen.        R2 may also be[(R6-0)n]-R7              where:            R6 may be a C1-C4-alkyl group which may also be branched, for example methyl, ethyl, propyl, isopropyl, butyl, isobutyl or tert-butyl.                    Alkylamido (meth)acrylates            m: 1-4            R7 may be the methyl group or the ethyl group.                        
Useful amines include the following compounds: Dimethylaminoethylamine, diethylaminoethylamine, dipropylaminoethylamine, diisopropylaminoethylamine, dibutylaminoethylamine, diisobutylaminoethylamine, dimethylaminopropylamine, diethylaminopropylamine, dipropylaminopropylamine, diisopropylaminopropylamine, dibutylaminopropylamine, diisobutylaminopropylamine, dimethylaminobutylamine, diethylaminobutylamine, dipropylaminobutylamine, diisopropylaminobutylamine, dibutylaminobutylamine, diisobutylaminobutylamine, methylamine, cyclohexylamine, dimethylaminohexylamine, diethylaminohexylamine.
Particular preference is given, in addition to dimethylaminopropylamine, to dimethylaminoethylamine, dimethylaminobutylamine, dimethylaminopentylamine and dimethylaminohexylamine.
2. Prior Art
The literature describes many batchwise transesterification processes (batch transesterification processes) in conjunction with different catalysts.
The search for economically more viable processes led to the discovery of continuous transesterification processes in which the reactants are fed continuously and the products are removed continuously. The continuous transesterification processes have the following advantages over the batchwise transesterification processes: the process can be more easily automated and can be operated with a reduced need for personnel, the product quality has better reproducibility and less variability, the plant capacity increases as a consequence of the absence of the sequential working through of the individual preparation steps (filling, reaction, low boiler removal, product removal, emptying). The process has a higher space-time yield than a batch process.
Continuous transesterification processes are known.
EP 0 960 877 (Elf Atochem S.A.) describes a continuous process for preparing methacrylate esters of dialkylaminoalcohols. Dialkylaminoalcohols are reacted generally with methyl (meth)acrylate to obtain dialkylaminoalkyl(meth)acrylate by the following process:
The mixture of the starting materials (methyl (meth)acrylate and dialkylaminoalcohol) is fed continuously together with a tetraalkyl titanate as a transesterification catalyst (for example tetrabutyl, tetraethyl or tetra(2-ethylhexyl)titanate) and at least one polymerization inhibitor (for example phenothiazine, tert-butylcatechol, hydroquinone monomethyl ether or hydroquinone) to a tubular reactor where the conversion is effected at a temperature of 90-120° C. to the dialkylamino (meth)acrylate while simultaneously continuously removing the azeotropic methyl (meth)acrylate/methanol mixture. The crude reaction mixture (crude ester) is fed to a first distillation column in which a substantially catalyst-free stream is removed under reduced pressure at the top of the distillation column, and the catalyst and also a little dialkylaminoalkyl(meth)acrylate are removed in the bottom of the distillation column. The top stream of the first distillation column is then fed to a second distillation column in which a stream of low-boiling products having a little dialkylaminoalkyl(meth)acrylate is removed under reduced pressure at the top and a stream consisting of mainly dialkylaminoalkyl (meth)acrylate and also polymerization inhibitor(s) is removed at the bottom and fed to a third distillation column. In the third distillation column, a rectification is carried out under reduced pressure in which the desired pure dialkylaminoalkyl (meth)acrylate ester is removed at the top and essentially the polymerization inhibitor or the polymerization inhibitors are removed at the bottom. The bottom stream of the first distillation column is recycled into the reactor after further purification with the aid of a film evaporator, just like the top stream from the second distillation column.
This process dispenses with dewatering of the alcohols before use, which may lead to increased deactivation of the tetraalkyl titanate used as a consequence of hydrolysis up to the formation of undesired solid deposits. In addition, the process has the disadvantage that the catalyst is thermally stressed at relatively high temperatures in the bottom of the first distillation column. This can easily lead to decomposition of the catalyst.
In this process, both the unconverted reactants and the product are rectified via the top twice altogether. This entails very high energy costs and a total of 4 rectification columns, some of which have to have very large dimensions. The process is therefore burdened with very high capital and operating costs.
EP 0 968 995 (Mitsubishi Gas Chemical Comp.) describes a continuous process for preparing alkyl(meth)acrylates using a reaction column. The transesterification reaction is effected directly in a distillation column (i.e. reactor and distillation column for removing the methyl (meth)acrylate/methanol azeotrope form one apparatus), to which the starting materials (methyl (meth)acrylate and alcohol) are fed continuously. The catalyst required, here likewise preferably a titanium compound, is disposed in the distillation column. In the case of a homogeneous catalyst, the catalyst is metered continuously into the distillation column. However, as a consequence of the flushing effect by the liquid reflux in the distillation column, the use of homogeneous catalysts in a distillation column leads to increased catalyst demand, and, when a solid catalyst precipitate occurs, to fouling of the column internals. In the case of a heterogeneous catalyst, the catalyst is disposed in the reaction column. However, the positioning of the catalyst in the distillation column is disadvantageous, because an increased pressure drop then occurs in the distillation column and very high cost and inconvenience is additionally associated with the regular cleaning of the distillation column. In addition, heterogeneous catalysts may deactivate for example as a consequence of undesired polymerization.
DE 4 027 843 (Röhm GmbH) describes a continuous process for preparing N-substituted (meth)acrylamides by transesterifying alkyl esters of (meth)acrylic acid with aliphatic and aromatic amines. The reaction temperature is >150°, the pressure approx. 160 bar. There is no catalyst.